/Engine/Plugins/Experimental/MeshModelingToolsetExp/Source/MeshModelingToolsExp/Public/MeshSelectionTool.h
Delete the selected triangles from the active Mesh Object and create a new Mesh Object containing those triangles
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(CallInEditor, Category=MeshEdits, Meta=(DisplayName="Separate", DisplayPriority=10)) void Separate()